The Breakthrough Starshot System Model (1805.01306v3)

Abstract: Breakthrough Starshot is an initiative to prove ultra-fast light-driven nanocrafts, and lay the foundations for a first launch to Alpha Centauri within the next generation. Along the way, the project could generate important supplementary benefits to solar system exploration. A number of hard engineering challenges remain to be solved before these missions can become a reality. A system model has been formulated as part of the Starshot systems engineering work. This paper presents the model and describes how it computes cost-optimal point designs. Three point designs are computed: A 0.2 c mission to Alpha Centauri, a 0.01 c solar system precursor mission, and a ground-based test facility based on a vacuum tunnel. All assume that the photon pressure from a 1.06 {\mu}m wavelength beam accelerates a circular dielectric sail. The 0.2 c point design assumes \$0.01/W lasers, \$500/m$^2$ optics, and \$50/kWh energy storage to achieve \$8.0B capital cost for the ground-based beam director. In contrast, the energy needed to accelerate each sail costs \$6M. Beam director capital cost is minimized by a 4.1 m diameter sail that is accelerated for 9 min. The 0.01 c point design assumes \$1/W lasers, \$10k/m$^2$ optics, and \$100/kWh energy storage to achieve \$517M capital cost for the beam director and \$8k energy cost to accelerate each 19 cm diameter sail. The ground-based test facility assumes \$100/W lasers, \$1M/m$^2$ optics, \$500/kWh energy storage, and \$10k/m vacuum tunnel. To reach 20 km/s, fast enough to escape the solar system from Earth, takes 0.4 km of vacuum tunnel, 22 kW of lasers, and a 0.6 m diameter telescope, all of which costs \$5M. The system model predicts that, ultimately, Starshot can scale to propel probes faster than 0.9 c.

• The paper presents a comprehensive system model optimizing mission design and cost, featuring a 4.1-meter sail for 0.2c missions and a 19-meter sail for precursor tests.
• The model integrates nested optimization algorithms and trajectory integration to balance key parameters such as laser, optics, and sail material properties.
• The analysis demonstrates that advanced photon propulsion can drive ultra-fast spacecraft speeds, paving the way for feasible interstellar exploration.

Review of "The Breakthrough Starshot System Model"

The paper "The Breakthrough Starshot System Model" by Kevin L. G. Parkin presents an intricate and comprehensive system model for the Breakthrough Starshot initiative—an ambitious project aimed at sending ultra-fast light-driven nanocrafts to Alpha Centauri. The model is a pivotal part of the project's systems engineering efforts to devise cost-effective mission designs, tackling some of the fundamental engineering challenges that still exist.

Parkin's model addresses the need for cost-optimized point designs for missions to Alpha Centauri at \SI{0.2}{c} and precursor solar system missions at \SI{0.01}{c}, as well as a ground-based test in a vacuum tunnel. These designs assume propulsion based on photon pressure exerted on a dielectric sail, propelled by a \SI{1.06}{\micro\meter} wavelength laser beam, thus revitalizing and expanding upon early ideas proposed by Robert Forward and other pioneers.

Key Methodological Considerations

The system model developed by Parkin incorporates several nested optimization algorithms and trajectory integration methods to ensure system-level cost minimization while facilitating feasible trajectory attainment for the sailcraft. Significant departures from previous models are evident, particularly those relying on closed-form solutions and manual optimization processes, as this model integrates a far broader array of variables and constraints, which results in more precise requirements and subsequently lower costs.

Central to the model's operations are several user-defined technology figures of merit for cost optimizations. The model is sensitive to these parameters, which are adjusted to either current or speculative future values depending on the mission type, whether it's a near-term precursor or a longer-term interstellar mission. The costs associated with lasers, optics, and storage are particularly noteworthy, as they drive the feasibility and scalability of the missions. Sail material characteristics, such as reflectance and absorptance, also play critical roles in defining the sailcraft's feasible acceleration profiles.

Numerical Results and Exploration of Design Parameters

The model's comprehensive approach yields several notable outputs:

• \SI{0.2}{c} Mission Design: The cost-optimal design proposes a 4.1-meter diameter sailcraft, accelerated over a period of \SI{9}{min} using \SI[per-mode=symbol]{0.01}[\$]{\per\watt} laser technology. This mission is indicative of a near-future technology landscape, presuming significant advancements and reductions in laser and optics costs. Capital expenditures for the beam system are estimated at \SI{10}{B}\$, highlighting the ambitious nature of this initiative.
• \SI{0.01}{c} Precursor Mission: Exhibiting the feasibility of lower-scale endeavors within the solar system, this mission design features a 19-meter diameter sailcraft, demonstrating the Starshot technology in an attainable scenario with a significantly reduced capital expenditure.
• Ground-Based Vacuum Tunnel Test: This venue is proposed for testing sail dynamics and beam-riding techniques, with flexible designs scaling phased dynamics under \SI[per-mode=symbol]{100}[\$]{\per\watt} lasers and a pragmatic \SI{2}{m} optics cost.

Implications and Future Directions

The paper underscored the capacity of Starshot systems to propel nanocrafts to velocities close to \SI{0.9}{c} with future cost and technological improvements. Practically, this has profound implications for the scope and nature of humanity's interstellar exploration capabilities. The immediate focus includes comprehensive R&D efforts directed towards the development of advanced dielectric sails with nanoengineered structures, further cost reductions in laser technology, and addressing beam-riding challenges with solutions that enable micro-steering capabilities within microsecond timescales.

Theoretically, the paper stimulates discussion on optimizing energy efficiency relative to relativistic constraints and sustainability within interstellar medium interactions. It sets the stage for future works intersecting materials sciences, opto-electronics, and interstellar propulsion dynamics.

Conclusion

Parkin’s model is a critical step in refining the technological and economic feasibility of Breakthrough Starshot missions. While challenges remain, the system model provides a robust framework to guide the evolution of the Starshot project towards its audacious objectives. Future iterations should encompass enhanced material characterization and broader integration of domain-specific models to secure a realistic pathway towards achieving these interstellar velocities.